Recently, white light emitting diode (LED) light sources including an LED have been actively studied as white light sources such as light sources for lighting apparatuses and back light sources for liquid crystal display apparatuses. An exemplary white LED light source is composed of a blue LED which emits blue light and a phosphor which converts the blue light from the blue LED into yellow light. Actively being studied blue LEDs are especially nitride semiconductor light emitting devices including a wide band gap semiconductor such as a nitride semiconductor.
In most blue LEDs in use, a light emitting layer which recombines electrons and holes and thereby emits light is formed on a crystal plane called a (0001) plane (a c-plane, a polar plane) composed of nitride semiconductor crystals. However, a light emitting layer formed on the c-plane causes polarization in the light emitting layer due to the difference in lattice constant between materials used therein. This polarization causes the problem that an internal electric field called a piezoelectric field generated in the light emitting layer spatially separates the electrons and holes, resulting in reduction in the light emission efficiency.
In order to solve this problem, trials have been conducted which are for reducing such influence of piezoelectric fields by forming a light emitting layer on a plane (non-polar plane) tilted with respect to the c-plane. However, such a non-polar plane has not yet been in practical use because of the need of large openings and high dislocation density. Examples of conventionally proposed blue LEDs including a non-polar plane include a nitride semiconductor light emitting device disclosed in Patent Literature (PTL) 1.
With reference to FIG. 18, the conventional method of manufacturing a nitride semiconductor light emitting device is described below. FIG. 18 shows schematic cross-sectional views of a conventional nitride semiconductor light emitting device in processes of a conventional manufacturing method.
As shown in (a) of FIG. 18, one of a silicon oxide film and a silicon nitride film is formed on a silicon substrate 1 which is oriented off by seven degrees from a (100) silicon plane, and a mask 52 which has stripe-shaped openings is formed using a photolithography method or a dry etching method.
Next, as shown in (b) of FIG. 18, wet etching potassium hydroxide (KOH), tetramethylammonium hydroxide (TMAH), or the like is performed on the silicon substrate 1 with the mask 52 formed thereon, so as to transform the silicon substrate 1 to have an uneven structure in which cuts having a triangle cross-section are formed at positions corresponding to the openings in the mask 52. At this time, slope faces in protrusions (recesses) in the uneven structure are facet faces 61 of the (111) silicon plane.
Next, as shown in (c) of FIG. 18, a mask 53 which is a silicon oxide film or a silicon nitride film is formed to cover one of two slope faces in each of the protrusions (recesses) using a sputtering method or a vacuum evaporation method.
Next, as shown in (d) of FIG. 18, a nitride semiconductor crystal is grown on the silicon substrate 1 using a Metal Organic Chemical Vapor Deposition (MOCVD) method, and a crystalline nitride semiconductor 2 is grown on only on each (111) silicon facet face 61 which is not covered by any of the masks 52 and 53. The crystalline nitride semiconductor 2 on each facet face 61 is grown in the growth direction to be a (1-101) facet face 70 in the nitride semiconductor 2.
This crystal growth further continues, and as shown in (e) to (g) of FIG. 18, nitride semiconductors 2 grown from the side faces of adjacent ones of the protrusions (recesses) are combined with each other, in other words, the (1-101) facet faces 70 in the nitride semiconductor 2 are combined to be the continuous (1-101) plane in the final nitride semiconductor 2.
Next, an n-type semiconductor layer, a light emitting layer, and a p-type semiconductor layer are formed on the crystalline nitride semiconductor generated in the above-describe manner. In this way, it is possible to manufacture a conventional nitride semiconductor light emitting device (not shown).